Optimization of β/near-β forging process parameters of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si by using processing maps

The isothermal and constant strain rate compression tests of titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si are conducted by Thermecmaster-Z simulator and the deformation behaviors at the temperature of 990 ∼ 1080 °C and strain rate of 0.001 ∼ 70 s- 1 are extensively investigated. The processing maps (P-maps) under these deformation conditions are constructed and the forging process parameters are then optimized based on the generated P-maps. The experimental results show that most of the deformation is located at the flow instability zone when the strain rate is high (ε̇ ≥ 0.6 s- 1). At the near-β forging temperature range, the feasible deformation conditions are (990 ∼ 1008 °C, 0.001 ∼ 0.01 s- 1) and its deformation mechanism is superplasticity. The optimum process parameters are (990 °C, 0.001 s- 1). At the β forging temperature range, when the deformation strain is smaller (ε̄ ≤ 0.7), the suitable deformation conditions are (1035 ∼ 1070 °C, 0.001 ∼ 0.08 s- 1). The optimum deformation parameters, however, are 1055 °C and 0.001 s- 1. If the strain is increased (ε̄ = 0.8 ∼ 1.2), there are two feasible deformation zones, viz., (1008 ∼ 1025 °C, 0.001 ∼ 0.02 s- 1) and (1025 ∼ 1050 °C, 0.008 ∼ 0.16 s- 1), respectively. At the β forging temperature range, the main deformation mechanism is dynamic recrystallization. Crown